son's nail problems

Hello all! This is my first time posting, so I hope I'm doing it right. My son is only four years old but for the last year he has had problems with the toenails on his left foot. It started with two nails and then slowly spreaded to the others. They started out looking broken, like they were smashed under a door but the more they grew, the worse they became. Now, two of the nails look to be very soft. Where the nail bed comes out, it is white and very soft to the touch. There is no longer a hard nail. We have taken him to a dermatologist and was told by his pediatrician, but the only thing he came up with was lichen planus. After doing some reading, it looked more like lichen striatus. Would a podiatrist be better? If anyone has information on what this might be, that would be great. He swims 3-4 times a week and I'm afraid it's making it worse. Please help....